Active microwave irises and windows

ABSTRACT

A waveguide thin film window or an iris fabricated from either a thin film or a conventional plate and mounted transverse to the flow of energy in a waveguide and electrically insulated from the waveguide. Diode switching means are provided for selectively disconnecting and connecting the window or iris to the walls of the waveguide.

United States Patent Low et al.

ACTIVE MICROWAVE IRISES AND WINDOWS Inventors: George M. Low,Administrator to the National Aeronautics and Space Administration withrespect to an invention of; Robert L. Ramey; Hugh S. Landes, both of'IIIIIIIIIIIIIIIA "II'III'III'I 5] Mar. 14, 1972 2,757,341 7/1956Lundstrom ..333/7 3,014,188 12/1961 Chester et al... .333/98 S X3,163,835 12/1964 Scott ..333/98 P OTHER PUBLICATIONS Southworth, G. C.Principles & Applications of Waveguide Transmission" Dvan Nostrand Co.1950, pp. 377- 380. Ramey et al. Microwave Properties of Thin Films WithApertures, M'IT- 18 N0. 4-4-1970 pp. 196- 204.

Primary Examinerl-Ierman Karl Saalbach Assistant Examiner-Wm. H. PunterAttorney-John R. Manning, Howard J. Osborn and William H. King [5 7]ABSTRACT A waveguide thin film window or an iris fabricated from eithera thin film or a conventional plate and mounted transverse to the flowof energy in a waveguide and electrically insulated from the waveguide.Diode switching means are provided for selectively disconnecting andconnecting the window or iris to the walls of the waveguide.

6 Claims, 2 Drawing Figures PATENTEDMR 14 I972 3,549,535

ROBERT L. RAMEY HUGH S. LANDES BY EUGEN M NUS ATTOR YS ACTIVE MICROWAVEIRISES AND WINDOWS ORIGIN OF THE INVENTION The invention describedherein was made in the performance of work under a NASA contract and issubject to the provisions of section 305 of the National AeronauticsSpace Act of 1958, public law 85-568 (72 stat 435, 42 USC 2457).

BACKGROUND OF THE INVENTION The invention relates generally towaveguides and more specifically concerns waveguide windows and irises.

This invention is applicable to both thin film and conventional irises.Thin film as used in this specification and claims include all filmthicknesses for which (a) the electrical conductivity of the film isless than the bulk conductivity of the same material, and (b) thethickness of the film is negligible when compared to the waveguidewavelength of the microwave signal. To be more specific, in the case ofall metal and semimetal films, a thin film includes all film thicknessesof less than 1,000 angstrom units even though the thickness can beseveral thousand angstrom units and still meet the definition. Lowconductivity semiconductors, on the other hand, could require athickness on the order of wavelength and therefore cannot be consideredas films. High conductivity semiconductors may be on the order of tensof thousands of angstroms in thickness and satisfactorily meet therequirement of being a thin film.

Conventional irises are usually electrically connected to the walls ofthe waveguide. However, if these irises are electrically disconnectedfrom the walls of the waveguide the transmission and reflectioncharacteristics of the irises materially change. Consequently, if meansare provided for selectively disconnecting and connecting the irises tothe walls of the waveguide the irises have many applications. It istherefore the primary purpose of this invention to provide means forselectively disconnecting and connecting conventional and thin filmirises and windows to the walls of a waveguide.

SUMMARY OF THE INVENTION The invention consists of a conventional or athin film iris or window in a waveguide with the iris or windowelectrically insulated from the walls of the waveguide by means of aninsulating material. Diodes are connected between the bottom of the irisor window and the bottom wall of the waveguide and between the top ofthe iris or window and the top wall of the wave guide through theinsulating material. Means are provided for selectively forward andreverse biasing these diodes to connect and disconnect the iris orwindow from the walls of the waveguide, thereby providing means forchanging the transmission and reflection characteristics of the iris orwindow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic drawing of theembodiment of the invention using a thin film iris without an aperture;and

FIG. 2 is a schematic drawing of the embodiment of the invention usingeither a thin film iris with an aperture or a conventional iris.

DETAILED DESCRIPTION OF THE INVENTION Turning now to the embodiments ofthe invention selected for illustration, the number 11 in FIG. 1designates a waveguide having a top, a bottom and two sidewalls. Locatedinside the waveguide and transverse to the flow of energy through thewaveguide is a thin film iris 12 that is electrically insulated from thewalls of the waveguide by an insulating material 13. A diode 14 has itscathode connected to the bottom of thin film l2 and its anode connectedthrough the bottom of waveguide 11 and a feedthrough capacitor 18 to aswitch 16. A diode has its anode connected to the top of thin film l2and its cathode connected through the top of waveguide 11 and afeedthrough capacitor 19 to switch 16.

Switch 16 is also connected across a battery 17. Feedthrough capacitor18 is connected to the bottom of waveguide 11 and feedthrough capacitor19 is connected to the top of waveguide 11. When switch 16 is in theposition shown, diodes 14 and 15 are reverse-biased and thin film 12 isthereby electrically disconnected from the top and bottom walls ofwaveguide 11. When switch 16 is in its other position, diodes l4 and 15are forward-biased and microwave energy flows from the thin film 12through diodes l4 and 15, and the feedthrough capacitors l8 and 19 tothe walls of the waveguide.

With switch 16 in the position shown, the two diodes are reverse-biasedand thin film 12 is entirely insulated from the walls of waveguide 11which results in a maximum power transmission through thin film 12. Withswitch 16 in its other position the two diodes are forward-biasedconnecting the bottom and top of thin film 12 to waveguide ll whichgreatly reduces the power transmission through the thin film. Byelectrically adjusting the forward bias current the power transmissionthrough the film may be controlled. For the principle TE mode inrectangular waveguides there are essentially no currents between the twosides of the film and the sidewalls ot' the waveguide. Therefore, thesetwo sides of the film can be left disconnected from the waveguide withno noticable change in power transmission.

The embodiment of the invention disclosed in FIG. 1 has several uses. Itcan be used as a switch modulator by controlling switch 16. With switch16 in the position shown the diodes are reverse-biased and there is anincreased transmission through the thin film. With the switch 16 in itsother position the diodes are forward-biased which decreases thetransmission through the film. Thus by controlling the conductivity ofthe diodes by means of switch 16 the invention can be used as amicrowave power transmission switch or modulator.

The embodiment of the invention in FIG. 1 can also be used as a powersplitter which operates on the principle of partial transmission throughthe thin film and partial reflection from the thin film. The powertransmission and power reflection of the thin film are both functions ofthe product of the film conductivity and the film thickness. Hence bycontrolling the product of the film conductivity and the film thicknes,any desired ratio of power transmission to power reflection can beobtained. Further, if desired, the transmision can be switched from alow value to a high value by disconnecting the film from the waveguidewalls. With the embodiment of the invention in FIG. 1 located at a teein the waveguide such that part of the microwave energy is reflected bythe thin film and part of it is transmitted through the thin film thenthe device can be used as a power splitter. That is, the transmittedpart of the energy will travel down one branch of the waveguide from thetee and the reflected part of the energy will travel down the otherbranch of the waveg$ide. By the use of switch 16 the amounts oftransmission and reflection can be varied.

The embodiment of the invention in FIG. 1 can further be employed tocouple a microwave cavity to a microwave system in which case it is acavity coupler. The thin film iris offers the advantage that no couplingiris is required as in the case of conventional cavity coupling systems.

In each of these three devices, the thin film iris offers a compact,low-cost device which may be produced with a large degree offlexibility. In the case when microwave diodes are employed to controlthe effects of the film, the advantages are not only small size and lowcost, but the desirability of electric control as contrasted to magneticcontrol currently used by existing devices of a similar nature. Electriccontrol offers small size and weight in the control of circuitry andfast response as compared to magnetic control systems.

The thin film in a microwave system is a passive transmission-reflectiontype coupling element which can be made into an active coupling elementas described in FIG. 1. Also, because of the ability of the thin film tosupport an electric field, it can be placed in the sidewalls or top orbottom walls of the waveguide to couple energy from one waveguide intoanother waveguide system. The principle of operation of this example andthe ones above is based upon the voltage drop that appears across thefilm because of a microwave current in the film. The electric fieldproduced by this voltage drop radiates energy into the coupled system aswell as back into the original waveguide system. This second componentof 5 radiated energy appears as reflection from the film. Although theefficiency of this method of coupling is not very high, it does offerpromise for use in directional couplers used in microwaveinstrumentation circuits.

The other embodiment of the invention disclosed in FIG. 2 differs fromthe embodiment disclosed in FIG. 1 only in that an aperture is employedto increase the amount of power transmitted over that which can behandled by the thin film iris. The film or conventional plate 21 with anaperture 22 is mounted exactly the same as the thin film iris 12 inFIG. 1. The exact shape and symmetry of the aperture is selected toprovide the impedance and power transmission desired when the iris isconnected to the walls of the waveguide. Whenever the iris 21 isdisconnected from the walls of the waveguide, the power transmissionthrough the iris increases from to 100 times and the impedance presentedby the iris is materially altered. The ability to switch thetransmission properties of the iris can be used to develop severaldevices such as modulators, phase shifters and slot radiators. If thediode bias current is controlled by a modulating signal, the iris canserve as a transmitting type modulator. Step phase shifters that areelectrically switched in accordance with this invention should have afaster response than the present magnetically switched phase devicesthat employ ferrites. Diode switching of thin films placed over theslots of a multislot radiation guide would permit electronic control ofthe radiated intensity and the radiated field pattern.

It is to be understood that the forms of the invention herewith shownand described are to be taken as preferred embodiments. Various changesmay be made in the shape, size and arrangement of parts. For example,equivalent elements may be substituted for those illustrated anddescribed herein, parts may be reversed, and certain features of theinvention may be utilized independently of the use of other features,all without departing from the spirit or scope of the invention asdefined in the subjoined claims. Transistors or other electronic devicescould be used in place of the diodes for switching. More than oneswitching device at the bottom and top of the waveguide could be used.Other electronic switching devices could be used in place of switch 16and means other than the feedthrough capacitors could be used to applythe biasing voltages to the diodes without departing from the invention.

What is claimed is: 1. An active microwave waveguide iris comprising: amicrowave iris located inside a waveguide transverse to the flow ofenergy in the waveguide; means for attaching said iris to the wall ofsaid waveguide and for electrically insulating the iris from the wallsof the waveguide; first switching means connected between said iris andone side of said waveguide through said insulating means fordisconnecting and connecting said iris to said one side of saidwaveguide; second switching means connecting between said iris and asecond side of said waveguide through said insulating means fordisconnecting the connecting said iris to said second side of saidwaveguide; and means for controlling said first and second switchingmeans to selectively disconnect and connect said iris to said one andsecond sides of said waveguide. 2. An active microwave waveguide irisaccording to claim 1 wherein said iris is a thin film without anaperture.

3. An active microwave waveguide iris according to claim 1 wherein saidiris is a thin film with an aperture.

4. An active microwave waveguide iris according to claim 1 wherein saidiris is a conventional conducting plate with an aperture. g

5. An active microwave waveguide ins according to claim 1 wherein saidfirst and second switching means are diodes.

6. An active microwave waveguide iris according to claim 5 wherein saidcontrol means include means for selectively applying a controlledreverse bias and a controlled forward bias to said diodes.

1. An active microwave waveguide iris comprising: a microwave irislocated inside a waveguide transverse to the flow of energy in thewaveguide; means for attaching said iris to the wall of said waveguideand for electrically insulating the iris from the walls of thewaveguide; first switching means connected between said iris and oneside of said waveguide through said insulating means for disconnectingand connecting said iris to said one side of said waveguide; secondswitching means connecting between said iris and a second side of saidwaveguide through said insulating means for disconnecting the connectingsaid iris to said second side of said waveguide; and means forcontrolling said first and second switching means to selectivelydisconnect and connect said iris to said one and second sides of saidwaveguide.
 2. An active microwave waveguide iris according to claim 1wherein said iris is a thin film without an aperture.
 3. An activemicrowave waveguide iris according to claim 1 wherein said iris is athin film with an aperture.
 4. An active microwave waveguide irisaccording to claim 1 wherein said iris is a conventional conductingplate with an aperture.
 5. An active microwave waveguide iris accordingto claim 1 wherein said first and second switching means are diodes. 6.An active microwave waveguide iris according to claim 5 wherein saidcontrol means include means for selectively applying a controlledreverse bias and a controlled forward bias to said diodes.